The wet compression test confirms you have low compression on cylinders 3 & 4.
It is also the reason you had smoke when you started. ( oil you used for the test, which had to burn out )

The noise you hear can be from what ever combustion air is passing.

When the car is idling and you remove the oil fil cap:
1. Are the oil coming out at standard idling rpm?
2. When someone ref the motor to about 2000 rpm, are there oil coming out?

If it is the rings as the wet test indicate, then you will see or feel oil coming out by the oil fil cap.
Make sure oil level is correct before testing this.

Abarth L said:

The noise you hear can be from what ever combustion air is passing.

When the car is idling and you remove the oil fil cap:
1. Are the oil coming out at standard idling rpm?
2. When someone ref the motor to about 2000 rpm, are there oil coming out?

If it is the rings as the wet test indicate, then you will see or feel oil coming out by the oil fil cap.
Make sure oil level is correct before testing this.

Click to expand...

Tested this also, before testing I checked oil level and filled it a little bit to get it max level. Tried opening oil fill gap when engine was running idle rpm and when it was running about 2K rpm. There wasn't visible differences between these states and I would say that it is not coming out for lot. When watching it to sun light that was coming from window, I was able to see some oil stream above the gap and some minor drops appeared on cam belt cover when gap was open. It's difficult for me to say is this normal or does it tell about some issue.

I also created a small video clip about test: https://youtu.be/OPLo-HRaRj4

Thanks for the video.

Best is to put the palm of your hand, no gloves and feel if there is air blowing out.
To determine if there is pressure build up from the sump.
If there is pressure build up you might start thinking of a new set of rings. ( Obviously not just rings but for another discussion )

The car is running now which is good but if it is the rings, then running for long like this will create carbon build up on the valves, which will then burn and not seat any more.

So when you have a chance again:
1. Monitor oil usage vs km's traveled.
If it is high and you still want it to last a bit, keep the revs low.
2. Check if there is a big power dip since, compared to before this and now.

I think you have done a great job so far by doing all the tests and recording it.

Had not time to play with it much today, just let it run a while and drove it on the ramps to prepare oil change maintenance. Also tested to cover oil filling hole by hand when engine was running idle. Can't say that it is making any pressure there and wasn't able to see any oil drops on my hand after the test.

I planned to use some internal engine clener ("Engine flush") next before changing new oil and filter to see if it helps to that knocking sound. Vehicle mileage is about 120K km and oil service has been done regularly for it. It feels strange if the engine would be very worn with this mileage. I know it has some oil usage and usually it takes 4K to 5K km when the oil level goes from max level close to min level and there's clear need for re-filling.

That is good news, not having high sump pressure.
Then it might lean to a gasket leak between cylinder 3 & 4.
I really hope it is not.
Sometimes water will then seep into the oil system.
So when you do the oil change, check what is the condition and colour of the oil.
If it is becoming white, then it is the gasketfor sure, which will also explain the low compression and sound.

.

Abarth L said:

Hi

Your problem lay with cylinder 3 & 4.
1. Either worn rings. ( Unlikely due to 1 & 2's good condition )
2. Head gasket between cylinder 3 & 4 leaking.
3. Valves burned by both cylinder 3 & 4.

Click to expand...

From where you are now, as Abarth L has suggested, I think you have a head gasket issue. Your cranking pressures are definitely pointing to something wrong .

Do you have any white smoke out of the exhaust ?

P.S. I'm glad we've put the timing belt worry to bed .

.

Some news for the day: Did engine internal cleaning (flush) operation yesterday with old engine oil. After the flush replaced oil and filter. Today decided to repeat cylinder compress test when replacing spark plugs. At this time I started from cylinder four which gave earlier very bad results. At this time there was very different sound when cranking and meter displayd 17,5 bars for cylider four. Tested next cylinder three and when cranking the pressure throw my meter to two pieces even I was pressing it hart to spark plug hole. At this point I stopped testing cylinder because I was lucky that I didn't get hit by meter pieces. Next installed new spark plugs and air filter to get engine tested next. When listening carefully I think the engine sound differs earlier sound on video clip:

https://youtu.be/8l0m44aEyDE
(Earlier: https://youtu.be/OPLo-HRaRj4)

JariR said:

when cranking and meter displayd 17,5 bars for cylider four]

Click to expand...

I am glad it does not sound like a diesel anymore ?
However 17.5 Bar for a motor with 120 000 km on, is way to high.
Maybe some liquid entered the gauge or combustion chamber resulting in less air that could compress, resulting in gauge to read high and self distruct..

What was the colour of the oil when you removed it?

I still think the head gasket is the problem.
If there were a long time that the car were driven without anti-freeze, it might have damaged the head gasket, or even overheating badly might warp the head.

Old oil color was almost black, there wasn't clear signs about coolant mixed to oil though there was a little shortfall in coolant expansion tank. I haven't also noticed any signs about over heating. It has also been pretty cold weather here recently and interior heater is set to warm all the time and it has been working well, so it tells that coolant has been circulating in the system. So if it is about head gasket in this case, there should be some strange things hapened with it. Has there been known issues with head gasket in these engines? Anyway, I'll give it a try next and take it back to use. I've to follow oil and coolant color intensified on next kilometers and if there will appear clear signs about head gasket issue, I'd say that it will be a game over for this Stilo.

When the oil is white, light grey in colour it has been contaminated with water for a while, so sounds like it is a new symptom.

No, the head gasket is not a problem on these cars.
Head gaskets go mainly due to 2 reasons:
1. Water rusting away the metal of the gasket. ( That's why anti-freeze is so important)
2. Overheating badly, which cause the head and / or block to warp, creating a weak spot where a leak can punch through.

I suggest monitoring closely the oil and water levels.
Either the noise is goig to come back worse or combustion air is going to enter the water system, which in turn is going to over pressurise and burst a pipe.

Changing the head gasket set together with head bolts, timing belt, tentioners and water pump might be a plan for the not so far future.

But it does sound nice now, looks good, standard and all. ?

Yeah, I'll do increased monitoring for liquid levels on next weeks. Either of those common reasons for head gasket failure haven't gone truth with this engine. Since we often have several minus degrees temperatures here on winter time, it's not an option to use engine without anti-freeze, always used 50%-50% water-anti-freeze mixture here. There were no signs about coolant in old oil color and it's not smoking usually. After cylinder wet-test there was blue smoke for a while caused about that oil in cylinder.